1. Field of the Invention
The present invention relates to computer implementable decision support systems for determining factory schedules and dispatching systems for determining job priorities. General methodologies within this field of study include advanced planning systems, optimization and heuristic based algorithms, constraint based programming, simulation, and autonomic control.
2. Description of the Related Art
The dispatching of production lots is a critical activity for smooth and reliable operation of a manufacturing system. Shop floor software scheduling systems are used to decide the sequence of a set of queued lots to dispatch to a given tool in the manufacturing line. For simple manufacturing systems, a first-in-first-out (FIFO) rule is often a reasonable choice. However, in semiconductor manufacturing, there are various tool-specific and lot specific scheduling attributes which make this a poor or infeasible choice. The invention relates to a new scheduling problem common to 300 mm semiconductor manufacturers, an associated mathematical model, and a method for deciding whether to determine a production schedule via optimization or real time dispatching. The method can also be generalized to other manufacturing environments and conditions.
Semiconductor manufacturing, and other manufacturing industries, rely on a variety of tool sets. Many tools (e.g., photolithography tools) process production lots one at a time. However, some operations (e.g., furnace) are batch operations which can process multiple production lots at a time. For example, a typical furnace may process up to 6 production lots at a time. However, it is not strictly a requirement that 6 lots be processed in each batch. This leaves open the opportunity to create smaller batches which can be released earlier, rather than waiting for a full batch of the lots to arrive. Releasing smaller batches, rather than waiting for a complete batch, can improve tool efficiency and processing time for lots. For instance, consider the following simple example. A furnace tool currently has a single lot in queue and no lots are projected to arrive for 6 hours. If the batch processing time is less than 6 hours, and there are no substantial variable costs per batch, then it is sensible to release a batch with a single lot to reduce its flow time, rather than have the lot wait in front of the idle furnace for 6 hours to construct a full batch.
There has been substantial study of scheduling in manufacturing operations in the operations research and industrial engineering literature (e.g., Baker—“Elements of Sequencing and Scheduling” 1994 describes several of the classical problems referenced in the scheduling literature).
Autonomic systems are systems that have the ability to automatically manage themselves and dynamically adapt to change, subject to a set of overall system objectives. These self-managing systems are able to react to changes that they sense in their environment without the need for human intervention. Autonomic principles have been applied to computing in both hardware and software areas.